The cholinergic pharmacology of schistosomes is being examined through the use of structurally-related acetylcholine analogs. Fluorescent dansylated analogs are being synthesized, having side chains resembling choline, homocholine, methacholine, etc., and with varying substituents on the terminal amino group. These compounds are used to label schistosomes; labeling of structures in the head and near the gut is seen. Quantitative comparisons are made of the labeling behavior of different compounds, using microfluorimetric methods. Nonfluorescent acetylcholine analogs are also tested in this system, by recording their ability to block the labeling induced by standard fluorescent compounds. Cholinomimetic and anticholinergic activity are also examined using an activity monitor. Cholinergic drugs cause paralysis of schistosomes, while anticholinergic drugs block the paralytic effects of carbachol. Structure-activity comparisons are also made in this system. Inhibition of enzymes metabolizing acetylcholine will be studied. Acetylcholinesterase and choline acetyltransferase are being measured in schistosomes, and the inhibitory potency of related compounds is being tested. It is hoped that these studies can be helpful in planning the design of selective blockers of cholinergic neurotransmission in schistosomes.